v0.1.14: added post.reroot(); fixed dx._voxelize_union()

[huangziwei]

fix: dx._voxelize_union() failed to exclude soma in the last release when include_soma=False.

It's an embarrassing update so short after the last, so I took this opportunity to add post.reroot, which is mostly for skeletons without a true soma (soma detection failed in skeletonize), in those cases the default pseudo-soma will not be ideal most of the time, so you might want to reroot the skeleton to another extreme node or a node ID of you choice:

skel_rerooted = skel.reroot(axis="z", mode="max")

or

skel_rerooted = skel.reroot(node_id=<node_id_of_your_choice>)